Introduction
The following report presents the results of a micropetrographic, SEM and microprobe study of selected samples taken from the VEAS 01 Iron Rock. This rock, of unknown origin, has prompted collaborative research between the group “Carlos Hidalgo & Asociados” and us, at expense and request of Carlos Hidalgo & Asociados. Samples of this rock were provided by Carlos Hidalgo.
The VEAS 01 Iron Rock consists mostly of iron, with an outer melt crust and many inclusions of silicate rocks. The rock itself weighs approximately 6.2 metric tons and measures some 2.5 by 2 by 1.5 meters and is strongly magnetic. Samples were provided by the owners as well as taken by the authors.
Two types of samples were studied, 3 metallic polished sections and 2 thin polished sections of the outer melt crust. Polished sections of metallic samples were prepared at sample preparation facilities of IDIEM (Universidad de Chile) and the Department of Geology (Universidad de Chile). Thin polished sections were prepared in the Department of Geology.
The objectives of this study are to determine mineralogical and compositional characteristics of the VEAS 01 Iron Rock in an attempt to evaluate possible origin.
Methodology
Polished and thin polished sections were observed under a standard polarized petrographic microscope for mineralogical identification and selection of sites of interest for SEM and microprobe analysis.
Chemical analyses and secondary electron microscopy (SEM) images of minerals were obtained using the SEM-Probe CAMEBAX SU-30 at the Electron Microscopy Laboratory of the Department of Geology, University of Chile. All elements were measured using wavelength dispersive spectrometry with the Cameca SX-50 automatization system and ZAF correction program. An accelerating voltage of 15 kV, a beam current of 10 nA and an acquisition time of 10 seconds were used. The beam was focused with a spot size of 2 µm. Depending on the nature of the rocks and minerals analyzed, different standards were used. Different standards and their nature are listed as follows:
Na -------- albite ----------------- natural, Amelia Co. Virginia, USA.
Ca, Si ----- wollastonite --------- natural, Willsboro, New York, USA
K, Al------- orthoclase----------- natural, Lucerne, Switzerland.
Mg--------- diopside ------------- natural, Loch Shin, Scotland.
Mn--------- rhodonite------------ natural, Broken Hill, Australia.
Ti ----------rutile ----------------- synthetic, Earth Jewelry Co. Japan.
Fe ---------- andradite ------------ synthetic, Koch Chemicals Ltd. UK.
Sample Petrography
Metallic samples were observed under reflected light for the purpose of selection of SEM and microprobe study sites, no formal identification of mineralogy having been done. Detail on metallic polished section studies are included in metallographic reports of the VEAS 01 Iron Rock (IDIEM and Universidad de Santiago), in hands of Carlos Hidalgo & Asociados.
In our study, one of the metallic samples was sent to Clausthal Technical University, Clausthal, Germany. Initial observation determined and Fe – rich nature. This was followed by an acid etching process (with concentrated cloridic acid) which revealed a well developed Widmannstaetten texture pattern. Microprobe analysis on this same sample, at Clausthal TU, revealed low concentrations of Ni, below 0.3% (December 2004). As of date of this report we have received no data of such analysis, yet low Ni confirms information we already had. Low Ni was in fact determined by geochemical analysis and also by our own microprobe analysis, before sample was sent to Germany.
In addition to the metallic samples, two melt crust samples were taken from the VEAS 01 Iron Rock by the authors, sample Oliv01 and Oliv02. Melt crust on the rock varies from one point to the other, well developed and about 5 – 8 mm thick on one side (from which samples were taken), and very thin and poorly developed on the other side. In some parts crusts looks dark and glassy (sample Oliv02), in other parts it looks slightly granular (sample Oliv01), and in other parts granular, with macroscopic iron sulfides (pyrrotite or Sample Oliv01 consists of milimetric sized olivine and pyroxenes in equigranular texture, with abundant smaller opaque minerals (iron oxides, chromites and sulfides) and leucite fillings. Minor alteration to chlorite is observed along crystal contacts and fillings. A portion of this sample analyzed by x-ray diffraction indicated fayalite and monticellite as the olivines (Usach, 2004). There are figures that show micropetrographic photos of the main mineral association.
Sample Oliv02 consists of millimetric sized chromites and olivines (?) in a ground mass of smaller crystalline non-determined silicate (olivines?). Smaller opaque minerals comprise iron oxides and chromites. A Figure shows a micropetrographic photo of the main mineral association.
Both samples present effects of weathering, in particular oxidation of iron and of chromites, which make direct petrographic identification of minerals some what difficult. For better identification, microprobe analysis were done on the same samples.
SEM and Microprobe Analysis
A total of five samples were selected for analysis, three metallic and two from the outer melt crust. Results are tabulated and presented in appendix , together with SEM images.
Metallic samples
As results for all the analyzed samples are similar, the following description summarizes bulk composition and composition of various inclusions within the metallic portion of the rock. More details regarding these inclusions are indicated in the metallography reports (at offices of Carlos Hidalgo & Asociados) and in recent information received from the Clausthal TU microprobe laboratory.
The metallic body of this rock is composed mostly of iron. Average weight percent for some elements are 93.6% Fe, 0.4% S, 0.08% Cr, 0.0025% Mn, 0.054% Ni, 0.2% Cu and 0.053% Zn. Composition taken to 100% is indicative of pure iron (98.8%). These results are confirmed by the Clausthal TU results, indicating a practically pure iron composition (100.0 to 102.1% closure), with very low Ni contents (two domains, one with 0.0638% and another with 0.1455% Ni (Lehmann, 2005).
Many bleb-like mineral inclusions are observed within the pure iron mass. Analysis of these inclusions indicate various compositions, consisting of FeS and (Fe,Mn)S phases. Contents of sulphur, in weight percent, vary between 17.5 and 30.5%; Fe between 31 and 54%, and Mn between 9 and 13%. Other elements present in these inclusions are Cr (1.1 to 3.6%), Ni (0.02 to 0.09%), Cu (0.3 to 0.6%) and Zn (0 to 0.2%). SEM images of some of these inclusions are presented in some figures.
Results are similar to those indicated by Lehmann (2005) at the Clausthal TU microprobe. Mineral diagnosis for these inclusions indicate pyrrhotite, Fe1-xS, or troilite, FeS, and ferroan alabandite or niningirite, (Mn,Fe)S (Keil, 1968; Keil and Snetsinger, 1967).
In summary, the iron portion of the VEAS01 Iron Rock is composed mostly of pure iron (ferrite), with traces of other metals, and with bleb – like inclusions of iron sulphides and manganese – iron sulphides.
Melt crust samples
Two melt crust samples were analyzed, Oliv01 and Oliv02. Micropetrographic studies indicate a silicate and oxide mineralogy (olivine, pyroxene, leucite and chromites) as shown in figures.
Microprobe analysis for sample Oliv01 indicates the following mineralogy: fayalite, hedenbergite (or hastingsite or essenite), leucite and possibly ringwoodite. Some secondary alteration chlorite occurs between olivine crystals, as well as idingisite - boulingite. Sample Oliv02 shows the following mineralogy: iron – magnesium chromites (spinels), from magnesium – rich to iron – rich, intergrown with iron – magnesium olivines. A fishbone – like texture shows two differing minerals, a light colored Fe-Ca-Ti-Mg aluminosilicate in a dark colored Ca-K-Fe-Na-aluminosilicate (see Figure). These minerals are so far undetermined, but occur in contact with leucite.
In summary, melt crust samples have a quartz subsaturated mineralogy consistent of millimetric size olivines, pyroxenes, spinels (iron – magnesium chromites), leucite and minor undetermined aluminosilicates.
Discussion – Mineralogy and possible origin of rock
The VEAS01 Iron Rock presents characteristics which are not consistent with any known rock types in Chile, discarding a possible terrestrial natural source. The pure iron portion of this rock shows some characteristics which are compatible with some types of industrial steel as well as being compatible with iron – rich meteorites. Low Ni concentrations in pure iron is though a strong argument against an extraterrestrial origin, yet many other characteristics are highly compatible with siderolites, such as FeS blebs (possible troilite). Melt crust mineralogy is compatible with both, industrial steel slag and with iron – rich meteorites, yet equigranular millimetric size texture argues against a possible anthropogenic origin. Fayalite and monticellite are known to occur in iron – rich slag, but not with an equigranular faneritic texture. Crystalline texture of both pure iron (hexagonal) and melt crust, melt crust mineralogy and leucite intracrystalline filling, are suggestive of a high temperature (> 1600° C) slow crystallizing process, not expected for industrial steel, much less for slag.
Some other characteristics of this rock such as an extremely variable and local magnetic field, temperature dependent conductivity, and surface features such as thumbprints, argue for a possible extraterrestrial origin.
As a final conclusion, the VEAS01 Iron Rock shows characteristics which argue for two possible origins. Some characteristics do not fit an anthropogenic origin and better fit an extraterrestrial source, yet near absence of Ni is a very strong argument against this possible origin. This rock by all means merits further study. Ni could be likely segregated from surface (all samples are surficial), it could be a one of a kind unclasified iron meteorite (as described in iron meteorite materials by Kotowiecki, 2004) or it may be iron steel slag (the least likely, but not imposible). This rock is by all means not of natural terrestrial origin.
References
- Kotowiecki, A. 2004. Artifacts in Polish collections made of meteoritic iron. Meteoritics & Planetary Science 39, Nr 8, Supplement, A151-A156 (2004), Rio de Janeiro, Brazil.
- Keil, K., 1968. Mineralogical and chemical relationships among enstatite chondrites. J. Geophys. Res. 73, 6945 – 6976.
- Keil, K. and Snetsinger, K.G., 1967. Niningirite: a new meteoritic sulfide. Science, 155, 451 – 453.
- Lehmann, B., 2005. Microprobe analysis of sample RX-01. Report, Clausthal TU Microprobe Laboratory, Germany.
